Metal ions copper complexes

The shift of the half-wave potentials of metal ions by complexation is of value in polarographic analysis to eliminate the interfering effect of one metal upon another, and to promote sufficient separation of the waves of metals in mixtures to make possible their simultaneous determination. Thus, in the analysis of copper-base alloys for nickel, lead, etc., the reduction wave of copper(II) ions in most supporting electrolytes precedes that of the other metals and swamps those of the other metals present by using a cyanide supporting electrolyte, the copper is converted into the difficultly reducible cyanocuprate(I) ion and, in such a medium, nickel, lead, etc., can be determined. 

Metal-ion catalysis has been extensively reviewed (Martell, 1968 Bender, 1971). It appears that metal ions will not affect ester hydrolysis reactions unless there is a second co-ordination site in the molecule in addition to the carbonyl group. Hence, hydrolysis of the usual types of esters is not catadysed by metal ions, but hydrolysis of amino-acid esters is subject to catalysis, presumably by polarization of the carbonyl group (KroU, 1952). Cobalt (II), copper (II), and manganese (II) ions promote hydrolysis of glycine ethyl ester at pH 7-3-7-9 and 25°, conditions under which it is otherwise quite stable (Kroll, 1952). The rate constants have maximum values when the ratio of metal ion to ester concentration is unity. Consequently, the most active species is a 1 1 complex. The rate constant increases with the ability of the metal ion to complex with 2unines. The scheme of equation (30) was postulated. The rate of hydrolysis of glycine ethyl... 

It is found that the hydrolysis of fluorophosphate esters is also accelerated by transition metal ions and complexes. This would be an observation of little general interest, except for the fact that fluorophosphate esters form one of the more commonly encountered types of nerve gases (Fig. 4-51). The hydrolysis of fluorophosphate esters is increased dramatically in the presence of copper(n) and other transition metal complexes, and this sug-... 

As a conclusion, we can say that the interlayer cations have an important role in the valine sorption mechanism. The total quantity of the adsorbed valine increases in the following order calcium-montmorillonite < copper-montmorillonite < zinc-montmorillonite. This order can be explained by the cumulative effect of the affinity of cations to the layer charges (Table 2.2) and the stability constants of metal ion-valine complexes in the solution (Table 2.11). 

Macrocyclic polythioethers form coordination compounds with many transition metal ions [55] and, owing to their moderate rr-acidity (intermediate between that of amines and phosphines), can exert a stabilizing effect on lower oxidation states of the encircled metal [56]. Copper complexes of thiacrowns have been widely investigated, even in view of the fact that they can be considered convenient models in the study of redox properties of cuproproteins (systems whose active site is a copper center bound to the thioether groups of methionine residues [57]). 

Auerbach (37) recorded with a diode laser in a thin film of a solvent-coated polymer-metal ion salt complex (e.g., poly-2-vinylpyridine-AgNO3). Using short-duration pulses (120 ns) of 820-nm light (10 mW), he showed that high reflectivity marks could be created that could be read with a lower power diode laser. The mechanism is believed to involve thermally induced electron transfer from the polymer to the metal ion forming localized metal areas (Ag + e — Ag°). The concept is not limited to silver salts of gold, copper, and tellurium can be used. Polymers other than vinylpyridine that can form charge-transfer complexes with metal ions should function as electron-transfer binders. 

Bacon, R. G. R., Pande, S. G. Metal Ions and complexes In organic reactions. XI. Reactions In pyridine between copper species and aryl halides. In particular between copper(l) oxide and 2-bromonltrobenzene. J. Chem. Soc. C. 1970, 1967-1973. 

There has been considerable interest in the chemistry of ternary complexes of copper(II) containing a bidentate aromatic nitrogen base such as 1,10-phen-anthroline (phen) or 2,2,-bipyridine (bpy) and a bidentate oxygen donor ligand or an amino acid,1 6 as some of these could possibly serve as models for enzyme-metal ion-substrate complexes. Two procedures are described below for the convenient, high-yield preparation of two such complexes. 

The first step in this new stain protocol employs copper acetate, a metal salt that is both a good fixative ( ) and a silver stain enhancer. The mechanism of copper s stain enhancement, in this and other silver stains, may be similar to its action in the biuret reaction (15.), in which a characteristic color shift, from violet to pink, is achieved by titrating peptides in the presence of copper ions. Copper complexes formed with the N-peptide atoms of the peptide bonds are primarily responsible for this reaction. There are also some number of secondary sites which may interact with copper. Any elemental copper formed may displace positive silver ions from solution as copper has a greater tendency to donate electrons than silver, indicated by its position in the electromotive series of the elements. Following the treatment with copper acetate, the membrane is sequentially soaked in a solution containing chloride and citrate ions and then in a solution containing silver nitrate. The membrane is then irradiated with light while it is in the silver nitrate... 

The rate of p-nitrophenyl caproate hydrolysis by modified PEI, containing imidazole groups in the presence of metal ions, increased in the sequence Mn, Ni, Zn, Co , Cu [92], Among the selected metals, a copper complex was shown to be most effective, the maximum rate being achieved at a [imidazole]/[copper] ratio of 2.75. 

Copper(II) has often been colorimetrically determined by its intensely blue ammonia complexes. The a diagram in Figure 9-1 shows that a similar situation occurs to that for the Fe(III)-SCN complexes, namely that a constant excess NH3 concentration will be required if the color is to be proportional to the Cu(II) concentration. Even more useful, now, is the use of EDTA in the determination of metal ions. Copper ion is often titrated in ammonia buffers. Let us examine the constants to see if quantitative complexing of Cu(II) by EDTA should occur in the presence of NH3. 

Zr(IV), and Ce(IV) as the central metal ion. Copper(II) porphyrins are among the most studied of the paramagnetic metalloporphyrins. The Cu(II) complexes show a low-temperature luminescence that arises from the and states that exist in thermal equilibrium. These two states are derived from the lowest excited triplet state on the porphyrin ring, which is split because of the presence of a unpaired electron on the Cu(II) center. Transient absorption measurements show that the ambient temperature excited-state decay times are lowered when a ligand is associated with the axial coordination positions of the tetracoordinate Cu(Il) porphyrin complex. The excited state lifetimes of Cu(II) porphyrin complexes in solution can be either dependent or independent of the temperature and solvent. For the octaethylporphyrin complex Cu(OEP) the excited state lifetime increases as the temperature is lowered, and also as the solvent polarity is increased. By contrast, the excited state lifetime of the tetraphenylporphyrin Cu(TPP) is insensitive to both the temperature and the polarity of the solvent. This difference in their photophysical behavior is likely due to a difference in the energy gap between the charge transfer state and the T/ T states in the pair of complexes. 

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